This invention relates to aluminum base alloys and more particularly it relates to an aluminum base alloy containing silicon, copper and magnesium and a method of semi-solid forming the aluminum alloy to provide a formed member or product having improved properties.
There is great interest in the use of semi-solid forming of aluminum alloys to improve both yield strength and tensile strength of formed products. The properties of the formed products are strongly influenced by selection of the elements comprising the aluminum alloy.
The references disclose that the properties are improved by different mechanisms. For example, U.S. Pat. No. 1,595,058 discloses an aluminum base alloy containing 3 to 15 wt. % Si, 0.5 to 3 wt. % Cu and 0.25 to 1 wt. % Mn having improved tensile strength, the properties improved by an alkali metal treatment.
U.S. Pat. No. 1,924,727 discloses an aluminum base alloy containing 3 to 8 wt. % Si, 0.5 to 3 wt. % Cu, 0.2 to 1.5 wt. % Mg and 0.3 to 2 wt. % Mn. The alloy is improved by the addition of manganese or nickel.
U.S. Pat. No. 4,808,374 discloses a method for producing aluminum alloy castings and the resulting product having improved toughness. An Alxe2x80x94Si or Alxe2x80x94Sixe2x80x94Cu alloy containing 4 to 24 wt % of silicon, iron and other incidental impurities, the balance being aluminum is melted, and the melt is heated to a temperature between 780xc2x0 C. and 950xc2x0 C. The melt is poured into a mold and solidified. Solution heat treatment and aging are then conducted. The process is suitable for an alloy containing 0.25 to 1.4 wt % of iron. In a preferred embodiment, the alloy consists essentially of 6 to 12 wt % Si, 2 wt % Cu, 0.2 to 0.4 wt % Mg and other incidental impurities, the balance being aluminum. The solution heat treatment is preferably carried out by heating between 525xc2x0-545xc2x0 C. for a period of 1 to 5 hours.
U.S. Pat. No. 5,028,393 discloses an Al-based alloy for use as sliding material, superior in fatigue resistance and anti-seizure property consisting, by weight, of 1-10% Zn, 1-15% Si, 0.1-5% Cu, 0.1-5% Pb, 0.005-0.5% Sr, and the balance Al and incidental impurities.
U.S. Pat. No. 5,338,168 discloses an oil pump comprises a casing of aluminum alloy and at least one rotor housed therein. The rotor is produced by powder metallurgy by a rapidly solidified aluminum alloy comprising, by weight, of 5 to 25% of Si, up to 15% of one or more alloy elements selected from the group consisting of 3 to 10% of Fe, 3 to 10% of Ni and 1 to 8% of Cr, and the balance of Al and inevitable impurities. The casing may be produced by powder metallurgy or ingot metallurgy with an aluminum alloy consisting essentially, by weight, of 5 to 25%, preferably 5 to 17%, of Si, 1 to 5% of Cu, 0.2 to 1.5% of Mg, 0.2 to 1% of Mn, and the balance of Al and inevitable impurities. The rotor and casing are so combined that the sum of the Si content of said rapidly solidified aluminum alloy for casing and that of said rapidly solidified aluminum alloy for rotor being equal to or more than 15 percent by weight.
U.S. Pat. No. 5,879,478 discloses an aluminum alloy for thixoforming with the composition (by weight): Si: 5%-7.2%, Cu: 1%-5%, Mg less than 1%, Zn less than 3%, Fe less than 1.5%, other elements  less than 1% each and  less than 3% in total, with % Si less than 7.5-% Cu/3, which, when reheated to the semisolid state to the point at which a liquid fraction ratio between 35 and 55% is obtained, has an absence of non-remelted polyhedral silicon crystals.
U.S. Pat. No. 2,811,439 discloses an aluminum casting alloy containing 2 to 5 wt. % Cu, 1.5 to 2.5 wt. % Fe, 0.2 to 2 wt. % Si, and 0.05 to 0.3 wt. % Ti.
U.S. Pat. No. 4,284,429 discloses an aluminum casting alloy consisting essentially of 5.0% to 22.0% silicon, 0.5 to 7.0% copper, 1.5 to 5.5% magnesium, 2.0 to 8.0% zinc, iron not over 1.35%, manganese not over 0.65%, nickel not over 0.50%, titanium not over 0.20%, and chromium and other residual elements not over 0.15%, balance aluminum.
U.S. Pat. No. 4,785,092 discloses aluminum brazing alloys for assembling aluminum heat exchangers by brazing which consist essentially of 4.5 to 13.5% of Si, from 0.005% to less than 0.1% of Sr and the balance essentially Al and, further, optionally may contain at least one element selected from the group consisting of 0.3 to 3.0% of Mg, 2.3 to 4.7% of Cu and 9.3 to 10.7% of Zn. The aluminum brazing alloys provide high strength brazed joints with highly refined microstructure and brazing operation can be performed in a good condition without causing any detrimental cavity. Such excellent properties make the brazing alloys especially suited for the fabrication of superhigh pressure heat exchangers.
U.S. Pat. No. 5,925,315 discloses an antifrictional aluminum alloy and a method for making an aluminum alloy without lead are provided. The alloy has improved tribological characteristics and a base composition, in weight percent as follows: silicon: 3.0-6.0, copper: 2.0-5.0, zinc: 0.5-5.0, magnesium: 0.25-0.5, nickel: 0.2-0.6, tin: 0.5-5.0, bismuth: 0.1-1.0, iron: up to 0.7, aluminum: essentially the balance.
U.S. Pat. No. 6,059,902 discloses an aluminum alloy containing Si: 1.5-12% (mass % here and hereinafter), Mg: 0.5-6% and, optionally, at least one of Mn: 0.5-2%, Cu: 0.15-3% and Cr: 0.04-0.35% and, further, containing Ti: 0.01-0.1% and the balance of Al and inevitable impurities, in which the average grain size of crystallized grains of Si system compounds is from 2 to 20 tm and an area ratio thereof is from 2 to 12%. The alloy is melted to obtain a cast ingot having DAS (Dendrite Arm Spacing) of 10 to 50 xcexcm, which is then put to a soaking treatment at 450 to 520xc2x0 C. and then to extrusion molding. The aluminum alloy has excellent machinability with no addition of low melting metals.
U.S. Pat. No. 5,911,843 discloses a process for casting, thermally transforming and semi-solid forming an aluminum base alloy into an article, the process comprising the steps of: casting a molten body of aluminum base alloy comprising 2 to 7 wt. % Si, 0.3 to 1.7 wt. % Mg, 0.3 to 3 wt. % Cu, 0.05 to 0.4 wt. % Fe, and at least one of the group consisting of 0.01 to 1 wt. % Mn, 0.01 to 0.35 wt. % Cr, max. 0.2 wt. % Ti, max. 0.3 wt. % V to provide a solidified body, the molten aluminum base alloy being solidified at a rate between liquidus and solidus temperatures of the aluminum base alloy to provide a solidified body having a dendritic microstructure.
U.S. Pat. No. 5,846,350 discloses a process for casting, thermally transforming and semi-solid forming an aluminum base alloy into an article, the process comprising the steps of: casting a molten body of aluminum base alloy comprising 2 to 5 wt. % Si, 0.3 to 1.7 wt. % Mg, 0.3 to 1.2 wt. % Cu, 0.05 to 0.4 wt. % Fe, and at least one of the group consisting of 0.01 to 1 wt. % Mn, 0.01 to 0.35 wt. % Cr, max. 0.2 wt. % Ti, max. 0.3 wt. % V to provide a solidified body, the molten aluminum base alloy being solidified at a rate between liquidus and solidus temperatures of the aluminum base alloy to provide a solidified body having a dendritic microstructure. Thereafter, heat is applied to the solidified body to bring it to a superheated temperature of 3xc2x0 to 50xc2x0 C. above the solidus temperature of the aluminum base alloy while maintaining the body in a solid shape, effecting thermal transformation of the body having the dendritic structure when the body is heated to above the solidus temperature. The body, having a non-dendritic structure, is formed in a semi-solid condition into the article.
U.S. Pat. No. 5,571,346 discloses a process for casting, thermally transforming and semi-solid forming an aluminum base alloy into an article, the process comprising the steps of: casting a molten body of aluminum base alloy to provide a solidified body, the molten aluminum base alloy being solidified at a rate between liquidus and solidus temperatures of the aluminum base alloy in a range of 5xc2x0 to 100xc2x0 C./sec. to provide an entire solidified body having a dendritic microstructure. Thereafter, heat is applied to the solidified body to bring the body to a superheated temperature of 3xc2x0 to 50xc2x0 C. above the solidus temperature of the aluminum base alloy while maintaining a body in a solid shape and effecting thermal transformation of the body having the dendritic structure when the entire body is uniformly heated to the superheated temperature. The body having a non-dendritic structure is formed in a semisolid condition into the article.
In spite of these disclosures, there is still a great need for a semi-solid formed member having improved properties such as tensile strength and yield strength properties.
It is an object of the invention to provide an improved aluminum base alloy suitable for forming in the semi-solid condition into members such as vehicular members having improved properties.
It is another object of the invention to provide an aluminum base alloy member or casting having improved properties in the T5 or T6 condition.
Yet, it is another object of the invention to provide a method for semi-solid forming an aluminum base alloy into articles or members having improved properties.
These and other objects will become apparent from a reading of the specification and claims appended hereto.
In accordance with these objects, there is provided a method of forming an aluminum base alloy member having a globular microstructure contained in a lower melting eutectic matrix. The method comprises providing a body of a semi-solid aluminum base alloy comprising 3.5 to 5.5 wt. % Si, preferably less than 5 wt. % Si, 3.6 to 5 wt. % Cu, 0.35 to 1 wt. % Mg, max. 0.25 wt. % Fe, max. 0.1 wt. % Mn, max. 0.25 wt. % Zn, and max 0.25 wt. % Ti, the balance aluminum, incidental elements and impurities. The method includes providing a mold for the alloy member and injecting the alloy in semi-solid form into the mold. The alloy is solidified in the mold to provide a member having a globular microstructure contained in a lower melting eutectic matrix. The member is aged in a temperature range of about 200xc2x0 to 400xc2x0 F. for a period of 1 to 24 hours. Prior to aging, the member may be solution heat treated in a temperature range of 800xc2x0 to 1000xc2x0 F. for 0.1 to 12 hours and then quenched.
The invention also includes an improved aluminum alloy member formed from semi-solid aluminum alloy comprised of 3.5 to 5.5 wt. % Si, preferably less than 5 wt. % Si, 3.6 to 5 wt. % Cu, 0.3 to 1 wt. % Mg, max. 0.25 wt. % Fe, max. 0.1 wt. % Mn, max. 0.25 wt. % Zn, and max. 0.25 wt. % Ti, the balance aluminum, incidental elements and impurities. The member can have a maximum grain size of less than 150 xcexcm, and a tensile strength in the range of 45 to 65 ksi and a yield strength of 40 to 55 ksi in the solution heat treated and aged condition.